The present invention relates to a rubber composition and a tire using the same.
In recent years, tires have been required to exhibit better steering stability and ride qualities, for example, a dependable braking performance while running at a high speed.
With respect to technologies to improve steering stability of tires formed from fiber cords coated with a rubber composition, a method to improve complex modulus (E*) of the rubber composition and thus rigidity of the tires is known in the prior art. More specifically, a method of compounding a phenol resin in the rubber composition is known. However, there is a problem that a rolling resistance (tan δ) of the rubber composition thus obtained is increased.
For improving complex modulus (E*) and decreasing rolling resistance (tan δ), a method of crosslinking a resorcin condensate or a modified resorcin condensate using a partial condensate of hexamethylolmelaminepentamethyl ether (HMMPME) or a partial condensate of hexamethoxymethylolmelamine (HMMM) is well known. However, in such a case, during processing of the rubber composition into sheets or toppings, crosslinking starts, resulting in increase of a viscosity of the rubber composition and making its processability unsatisfactory.
Also, for improving complex modulus (E*) and decreasing rolling resistance (tan δ), an another method of blending a large quantity of sulfur or a vulcanization accelerator is known. However, the rubber composition thus prepared provides tires with unfavorable durability because of marked natural hardening during running.
Furthermore, in response to consumers' demands for tires assuring low fuel consumption, technologies for reducing fuel consumption have been actively developed in recent years by means of improvement on a tread or a sidewall.
As a result of progress in improvement for low fuel consumption associated with improvement of such large size elements as the tread and sidewalls, cord topping rubber becomes more important for further advancement of reduction of fuel consumption.
Although FEM analyses show that reduction in rolling resistance (tan δ) is effective in making the cord topping rubber contribute to low fuel consumption, no effective technologies to lower the rolling resistance (tan b) have been developed yet.
In reducing rolling resistance (tan δ), for example, a method of decreasing the content of carbon black or, on the contrary, a method of increasing the content of oil is known. However, when the content of carbon black is reduced, the rubber composition thus prepared has deteriorated breaking properties. When the content of oil is increased, in addition to deterioration in the breaking properties, durability of the rubber composition is also deteriorated due to migration of oil to such adjacent elements as sidewalls, an inner liner and cushion rubber.
JP2004-217817A discloses a rubber composition which comprises a compound capable of donating methylene groups and a resorcin resin, and are suitable for use at breaker edges. However, since the rubber composition comprises only a natural rubber and/or isoprene rubber as the rubber component and has a large content of sulfur (4 to 6 parts by weight), deterioration in physical properties is caused by reversion during vulcanization under high temperature. Therefore, improvements are still required.
An object of the present invention is to provide a rubber composition with an adequate level of hardness, and excellent processability, rolling workability, low fuel consumption, elongation at break, complex modulus, and durability, and another object of the present invention is to provide a tire using the rubber composition.